Laser diodes have found increasing usage as optical transmitters in fiber optic communications systems. In such systems, the laser diode is typically driven by a constant current from an on-chip laser driver. In some optical transmission systems, an external DC to DC converter may be used to provide a fixed supply voltage for the laser diode from a main input voltage. However, this solution is not ideal. For example, a fixed DC converter output does not compensate for the burn-in characteristics or temperature drift of the laser diode over time. Additionally, if the laser diode is operating at high frequencies, the modulation current in the laser driver can change at high speeds and the DC converter will not be able to adjust the supply voltage to provide sufficient headroom voltage for the laser diode as more or less modulation current flows into the laser and the voltage drop across it changes accordingly.
The power dissipated on or in the laser driver may be calculated as the constant current multiplied by the headroom across it. Unfortunately, the headroom voltage is not optimized in a typical system, which wastes power. It would improve the whole system efficiency if an optimized and continuously updated headroom voltage for the laser diode could be determined and applied. Besides the advantage of efficiency, an optimized and continuously updated headroom voltage would also automatically compensate for the I-V curve drift over the lifetime of the laser diode and changes due to temperature variations to keep the bias current constant.